1. Field of the Invention
The present invention relates to a medical implantable lead of the kind being adapted to be implanted into a human or animal body for monitoring and/or controlling of an organ inside the body, comprising in a distal end a combined fixation means and electrode member in form of a helix, which is rotatable in relation to the lead and extendable out from the distal end by rotation of a tubular torque transferring member being connected to a rotatable control member in a proximal end of the lead, and which is adapted to fixate the distal end of the lead to the organ by being screwed into the tissue by rotation of the control member and the tubular torque transferring member, wherein the helix is electrically connected to a connector in the proximal end by means of at least one electrically conducting wire
2. Description of the Prior Art
It is well known in the art to use a medical implantable lead of the above kind to monitor and/or control the function of an organ inside a human or animal body, for example to monitor and/or control a heart by means of a monitoring and/or controlling device in form of a pacemaker or cardiac defibrillator connected to the proximal end of the lead. The medical implantable lead is provided with at least one electrical conductor, in form of a coil having one or more helically formed electrically conducting wires, sometimes also referred to as filars, which electrically connects one or more connectors arranged in the proximal end of the lead with one or more electrodes in its distal end. At least one of the electrodes is adapted to be in contact with the tissue of the organ for receiving and/or transmitting electrical signals from and/or to the organ and transmit them, through the electrically conducting coil, to the monitoring and/or controlling device connected to a connector in the proximal end of the lead. For attaching the distal end of the lead to the organ, the lead is provided with a helix, which can be rotatably extended out from the distal end of the lead and accordingly screwed into the tissue of the organ. To accomplish the rotation of the helix, it is mechanically connected to the innermost one of the electrically conducting coils, which accordingly has to be rotatable in relation to the lead as well as be sufficiently rigid to be able to transmit the required torque from the proximal to the distal end. The helix also functions as an electrode, which is penetrated into and embedded within the tissue. The helix may also be provided with one or more additional electrodes separate from the helix and e.g. be formed as a contact electrode, abutting against a surface of the organ, or be formed as a so called indifferent electrode which is surrounded by body fluids such as blood.
Normally, such medical implantable leads are not considered to be compatible with Magnetic Resonance Imaging (MRI), i.e. persons or animals having such a lead implanted into the body, are excluded from being examined by MRI-scanning. This is due to the fact that the electromagnetic field, that is generated during the MRI-scanning, will induce a current in the conductor, which connects the one or more electrodes in the distal end of the medical implantable lead with the monitoring and/or controlling device in the proximal end of the lead. This induced current may cause heating at an electrode being in contact with the tissue of the organ. If the heating is too high, there is a risk that this will cause damages to the tissue. However, the use of MRI-scanning for diagnostics is growing extensively and an increasing number of the population having a lead implanted would benefit from MRI-scans. It is thus desirable to reduce any heating at or close to the lead tip to acceptable and safe levels to allow MRI-scanning also of persons or animals having such a lead implanted.
It is known in the art to provide such medical implantable leads with an electrical shielding, in form of a tube of braided wires, which surrounds the coil and which in its proximal end normally is connected to the casing of the monitoring and/or controlling device. However, such shielded medical implantable leads are associated with several disadvantages. On the one hand, the braided shielding will give the medical implantable lead an increased thickness as well as increased rigidity, which normally is not desirable. On the other hand, it has appeared that such a braided shielding cannot prevent the induction of electrical current to the coiled conductor in a degree that is sufficient to, without risk, expose an individual, having an implanted lead, to a MRI-scanning.
U.S. Pat. No. 5,217,010 discloses a way to reduce heating caused by induced current from MRI-scanning by placing inductors close to the electrodes to limit currents through the electrodes. Such a prior art medical implantable lead comprises passive electronic components, which contribute to making the lead more complex and thus more costly to manufacture.